In fabrication of semiconductor devices, resist patterns are used as masks for ion implantation and pattern etching.
With respect to such resist patterns obtained by photolithography and transfer patterns formed from the resist patterns by etching, it is known that variations in dimensional accuracy may occur due to various factors such as process conditions, arrangement densities of the patterns, and underlying conditions. Such variations in dimensional accuracy may cause defects such as short-circuit between the patterns and disconnection of the patterns.
In recent years, an attempt has been made to obtain transfer patterns closer to design patterns by correcting designed pattern in accordance with a so-called optical proximity effect correction (hereinafter, referred to as “OPC”) method. One type of the OPC method is known as a rule-based OPC, wherein a correction amount corresponding to both a line width of each pattern portion of a design pattern and a space width of a space portion adjacent to the pattern portion is extracted by searching a previously prepared correction table, and the pattern portion is corrected by the correction amount thus extracted.
One specific method of extracting a correction amount corresponding to each pattern portion of a design pattern by using the rule-based OPC method is known as that using a DRC (Design Rule Checker). In the method using the DRC, each pattern having a target line width or each space portion having a target space width is extracted by setting a flag at an edge of a design pattern, depicting a circle having a radius equivalent to a target distance (target line width or target space width) around the flag, and sampling a portion with its edge portion contained in the circle as a target pattern portion or a target space portion. Each pattern portion of the design pattern is then corrected by a correction amount corresponding to both the sampled pattern portion and the space portion.
The method of extracting the target pattern portion and the target line width portion using the DRC, however, has the following problem. Referring to FIG. 14, at a portion between two pattern portions 101, in which the space width is changed between target space widths S1 and S2, according to the method using the DRC, a calculated edge portion, which is extracted as that having the target space width S1, is protruded outwardly from an actual edge portion. Accordingly, the portion in which the space width is changed between the values S1 and S2 cannot be accurately corrected. In other words, there may occur a partial deviation between the correction amount given to the above portion and a correction amount required for the portion.
In the case of forming a transfer pattern on a substrate by photolithography using an exposure pattern corrected on the basis of the above-described erroneous extraction, there may occur a defect such as short-circuit or disconnection of the transfer pattern at the above-described portion partially deviated from the design pattern. Up until now, it has failed to certainly solve the above-described problem of the method using the DRC.
In view of the foregoing, an object of the present invention is to provide an exposure pattern forming method capable of forming an exposure pattern by accurately correcting a design pattern, and to provide an exposure pattern formed by the method.